My understanding about a cloud provider lock in that it is a well thought-out, conscious decision (at least it should be) and after you made that step, you can

My understanding about a cloud provider lock in that it is a well thought-out, conscious decision (at least it should be) and after you made that step, you can use the specific services of the given cloud provider and you never move out. Are those hybrid/mixed cloud solutions or move between cloud provider viable or that common? Is there anybody went through a huge cloud migration which went well? If you need to move, there are huge amount of data you have to move for example between S3 and Google Cloud Storage, is that even possible to do beyond an early stage? I can't imagine.